Ordinary, currently used integrated circuits are substantially square semiconductor wafers approximately 1 cm on a side and capable of carrying up to 500 peripheral terminals. The TAB carrier of such an integrated circuit includes an insulating substrate carrying a plurality of radiating leads, known as a TAB lead frame. Ordinarily the substrate is made of a flexible plastic material, such as that known by the registered trademark Kapton, and is composed of one or more concentric frames. The leads of the carrier converge toward a central region of the substrate so as to be connected to the input/output terminals of the integrated circuit, in an operation known as ILB or inner lead bonding, ordinarily consisting in welding by thermocompression. The TAB carrier of an integrated circuit is typically cut from a film of the cinematography type, known as TAB film, that includes a longitudinal series of TAB lead frame, with holes along the edge for displacing and positioning the film.
One current problem in encapsulating a VLSI chip in a package relates to supplying energy to the chip. The supply potentials are ground, and ordinarily one or two different predetermined values. During chip operation, these potentials must remain stable despite the various values in intensity of the current required by the circuits called upon to function in the integrated circuit. As a result, the supply leads function as electrical transmission lines, having a reactive self-induction component in response to the variations in current. The self-induction component of each lead is accordingly proportional to its length. On the other hand, the present supply current intensity is high. For example, certain integrated circuits can instantaneously dissipate up to 6 watts at a voltage of up to 3 volts, thus requiring a flow of 2 amps. Considering the great density of the terminals of the chip, the leads must be narrow and quite close to one another. The flow of high-intensity supply current must accordingly take place in a plurality of supply leads. Moreover, the small cross sections of the leads increase their ohmic resistance.
The solution currently adopted comprises applying the supply potentials to respective solid terminals that are outside the package and are connected inside it to various potential conductor planes. The potential planes are associated with separate decoupling capacitors incorporated in the package, or form the plates of a decoupling capacitor. They are connected to the corresponding supply leads in the closest part of the integrated circuit. The length of the supply leads is thus reduced approximately to the length separating the supply terminals of the integrated circuit from the neighboring potential planes. This solution thus has the advantage of lowering the ohmic impedance and the reactive self-induction component of the supply circuit in the package. In the end, in fact, only the signal leads are long and extend over the entire carrier for connection to outside the package.
Using TAB carriers with short supply leads and long signal leads presents the problem in practice of signal interference circulating in the neighboring leads. In effect, on a high-density TAB carrier two large neighboring signal leads are substantially parallel and very close to one another (50 to 100 .mu.m apart) and comprise two electrical lines interacting with one another. One solution would be to distribute the signal leads in a plurality of groups insulated from one another by fixed potential conductors, such as the supply conductors. However, lengthening the supply leads to make electromagnetic shielding elements between two adjacent groups of signal leads would again present the problem of the reactive self-induction component of these long supply leads.